High frequency radio signal classifications

ABSTRACT

Examples include classifying high frequency radio signals. Some examples include receiving a fast Fourier transform (FFT) of a high frequency radio signal, determining a first signal strength at a first guard frequency bin, determining a second signal strength at a second guard frequency bin, and determining a third signal strength at a direct current carrier frequency bin. Examples also include classifying the high frequency radio signal based on the first signal strength, the second signal strength, and the third signal strength.

BACKGROUND

Long Term Evolution (LTE) may transmit signals in the unlicensed highfrequency radio spectrum, such as in the 5 GHz frequency ranges. TheseLTE signals may interfere with other signals, such as Wi-Fi, thattransmit in the same frequency ranges.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description references the drawings, wherein:

FIG. 1 is a block diagram of a computing device to classify a highfrequency radio signal, according to some examples.

FIG. 2 is a block diagram of a computing device to classify an RFsignal, according to some examples.

FIG. 3 is a block diagram of a Wi-Fi access point that classifies RFsignals, according to some examples.

FIG. 4 shows LTE and Wi-Fi FFTs, according to some examples.

FIG. 5 is a flowchart of a method of classifying a high frequency radiosignal, according to some examples.

FIG. 6 is a flowchart of a method of classifying a 5 GHz signal using anFFT with a resolution of at least 100 KHz, according to some examples.

FIG. 7 is a flowchart of a method of classifying a 5 GHz signal using anFFT with a resolution lower than 100 KHz, according to some examples.

DETAILED DESCRIPTION

Many different types of technologies transmit information wirelesslythrough the transmission of radio waves in the radio frequency spectrum.However, much of the radio frequency spectrum is regulated by governmentbodies, such as the Federal Communications Commission (FCC). To accessregulated areas of the spectrum, a license shall be approved by thegovernment bodies, e.g., FCC. This area of the radio frequency spectrumis considered the licensed spectrum. Due to limits in the licensedspectrum, technologies that typically operate in the licensed spectrumare beginning to broaden and move into the unlicensed spectrum.

For example, cellphone providers have generally operated Long TermEvolution (LTE) in the providers' licensed spectrum, an area of theradio spectrum that is exclusively licensed to the cellphone providers.However, in an effort to boost coverage in cellular networks, theseproviders are beginning to expand their LTE network by operating theirnetwork in the unlicensed 5 GHz spectrum range.

The broadening of these technologies into the unlicensed spectrum maycause disruption to technologies that have historically operated in theunlicensed spectrum. For example, an IEEE 802.11a compliant Wi-Fiequipment may operate in the 5 GHz spectrum. The Wi-Fi equipment may beused in the operation of wireless local area networks (WLAN), etc. Thus,the operation of an LTE network in the unlicensed 5 GHz spectrum maycause disruption and interference in the Wi-Fi signals due to mediumsharing, resource allocation, etc.

While LTE attempts to be a fair neighbor to Wi-Fi by sensing Wi-Fitransmissions and adapting accordingly, often times, LTE is unable tosee Wi-Fi signals in dense Wi-Fi deployments. This may be due to the twotechnologies being unable to decode each other's signals or packets.Accordingly, the LTE access point may degrade a Wi-Fi signal withouteven being aware that it is doing so. A Wi-Fi access point may be unableto respond or adapt when it cannot detect an interfering LTE signal.

Examples disclosed herein address these challenges by providing a wayfor a network device, such as an access point, to classify interferinghigh frequency radio signals. In some examples, the network device mayreceive a fast Fourier transform (FFT) of a signal. It may analyze thefast Fourier transform (FFT) of the signal to classify the signal,focusing on areas in the FFT where Wi-Fi and LTE signals differ. In someexamples, Wi-Fi and LTE signals differ in their behavior at their guardbands and at the direct current (DC) carrier. Accordingly, examplesdisclosed herein may determine the signal strengths at frequency bins inthe FFT corresponding to these locations and classify the signal basedon those signal strengths. Thus, examples disclosed herein provide a wayfor a Wi-Fi access point to understand whether a signal is an LTE signalwithout having to decode the LTE signal. This may make it possible forWi-Fi access point to adapt accordingly in light of an interfering LTEsignal.

In some examples, a computing device is provided with a non-transitorymachine-readable storage medium. The non-transitory machine-readablestorage medium includes instructions, that, when executed, cause aprocessing resource to receive a fast Fourier transform (FFT) of a highfrequency radio signal. The FFT comprises a direct current carrierfrequency bin, a first guard frequency bin lower than the direct currentcarrier frequency bin, and a second guard frequency bin higher than thedirect current carrier frequency bin. The storage medium also storesinstructions, that, when executed, cause the processing resource todetermine a first signal strength at the first guard frequency bin,determine a second signal strength at the second guard frequency bin,determine a third signal strength at the direct current carrierfrequency bin, and classify the signal. The classification is based onthe first signal strength, the second signal strength, and the thirdsignal strength.

In some examples, a computing device is provided with a non-transitorymachine-readable storage medium. The non-transitory machine-readablestorage medium includes instructions, that, when executed, cause aprocessing resource to receive a fast Fourier transform (FFT) of a highfrequency radio signal, determine a maximum strength of the FFT, anddetermine a number of peaks in the FFT that exceeds a first threshold.The storage medium also includes instructions to determine a firstsignal strength at a first guard frequency bin and a second signalstrength at a second guard frequency bin. This is in response to adetermination that the maximum signal strength exceeds the firstthreshold and the number of local peaks exceeds a second threshold. Thestorage medium also includes instructions, that, when executed, causethe processing resource to determine a third signal strength at a directcurrent carrier frequency bin in response to a determination that thefirst signal strength and the second signal strength meet a thirdthreshold. The storage medium also includes instructions, that, whenexecuted, cause the processing resource to classify the radio frequencysignal based on the third signal strength.

In some examples, a method is provided including receiving, at a networkdevice, a first FFT of a high frequency radio signal; determining, bythe network device, a first maximum strength of the first FFT; anddetermining, by the network device, a first number of local peaks in thefirst FFT that are above a first threshold. The method also includesreceiving, at the network device, a second FFT of the high frequencyradio signal; determining, by the network device, a second maximumstrength of the second FFT; and determining, by the network device, asecond number of local peaks in the second FFT that are above the firstthreshold. The method additionally includes determining, by the networkdevice, an average FFT based on the first FFT and the second FFT inresponse to a determination that the first maximum and the secondmaximum both meet the first threshold and the first number and thesecond number both meet a second threshold. The method also includesclassifying, by the network device, the high frequency radio signalbased on a signal strength of the average FFT at a first guard frequencybin, a signal strength of the average FFT at a second guard frequencybin, and a signal strength of the average FFT at the direct currentcarrier frequency bin.

Referring now to the figures, FIG. 1 is a block diagram of a computingdevice 100 to classify a high frequency radio signal. As used herein, ahigh frequency radio signal is a radio signal of at least 2.4 GHz. Insome examples, a high frequency radio signal is a radio signal of atleast 5 GHz. In some examples, the high frequency radio signal operatesin an unlicensed portion of the radio frequency spectrum. Many types ofwireless communication technologies (e.g., Wi-Fi, Long Term Evolution(LTE), etc.) operate in these high frequencies. Accordingly, computingdevice 100 may detect and classify one type of high frequency radiosignal from another type (e.g., classify a signal as being one type asopposed to another type). In some examples, the types of signals thatcomputing device 100 may classify between are LTE signals and Wi-Fisignals.

As used herein, a “computing device” may be a server, a network device(e.g., an access point, etc.), chip set, desktop computer, workstation,or any other processing device or equipment. In some examples, computingdevice 100 may be a Wi-Fi access point.

Computing device 100 includes a processing resource 101 and amachine-readable storage medium 110. Machine readable storage medium 110may be in the form of non-transitory machine-readable storage medium,such as suitable electronic, magnetic, optical, or other physicalstorage apparatus to contain or store information such as instructions111, 112, 113, 114, 115, related data, and the like.

As used herein, “machine-readable storage medium” may include a storagedrive (e.g., a hard drive), flash memory, Random Access Memory (RAM),any type of storage disc (e.g., a Compact Disc Read Only Memory(CD-ROM), any other type of compact disc, a DVD, etc.) and the like, ora combination thereof. In some examples, a storage medium may correspondto memory including a main memory, such as a Random Access Memory, wheresoftware may reside during runtime, and a secondary memory. Thesecondary memory can, for example, include a non-volatile memory where acopy of software or other data is stored.

In the example of FIG. 1, instructions 111, 112, 113, 114, and 115 arestored (encoded) on storage medium 110 and are executable by processingresource 101 to implement functionalities described herein in relationto FIG. 1. In some examples, storage medium 110 may include additionalinstructions, like, for example, the instructions to implement some ofthe functionalities described in relation to computing device 200 inFIG. 2 or Wi-Fi access point 300 in FIG. 3. In other examples, thefunctionalities of any of the instructions of storage medium 110 may beimplemented in the form of electronic circuitry, in the form ofexecutable instructions encoded on machine-readable storage medium, or acombination thereof.

Processing resource 101 may, for example, be in the form of a centralprocessing unit (CPU), a semiconductor-based microprocessor, a digitalsignal processor (DSP) such as a digital image processing unit, otherhardware devices or processing elements suitable to retrieve and executeinstructions stored in a storage medium, or suitable combinationsthereof. The processing resource can, for example, include single ormultiple cores on a chip, multiple cores across multiple chips, multiplecores across multiple devices, or suitable combinations thereof. Theprocessing resource can be functional to fetch, decode, and executeinstructions 111, 112, 113, 114, and 115 as described herein.

Instructions 111 may be executable by processing resource 101 to receivea fast Fourier transform (FFT) of a high frequency radio signal. Thesignal may be comprised of many frequencies components within a specificbandwidth. For example, the lowest-frequency signal component of thesignal may be 5150 MHz and the highest-frequency signal component may be5170 MHz. Thus, this signal ranges from 5150-5170 MHz and has abandwidth of 20 MHz. An FFT is a representation of a time/space signalin its frequency domain, where the FFT provides both magnitude and phaseinformation of the signal. In some examples, an FFT of a signal may bedetermined using samples of the signal and a Fourier transform. In someexamples, the signal is sampled at discrete points and thus, the FFTprovides magnitude readings at discrete points, called frequency bins.

As used herein, a frequency bin may be an arbitrary number thatcorrelates to a specific frequency or frequency range in the signal. Thelowest frequency bin in an FFT may correspond to the lowest frequency inthe frequency band of that signal; the highest frequency bin maycorrespond to the highest frequency in the band of that signal; themiddle frequency bin may correspond to the middle frequency in the band;etc. Thus, the order of the frequency bins in the FFT may correspond tothe order of the frequencies in the signal. For example, 512 discretepoints of a signal may allow for an FFT with 256 frequency bins. In a 20MHz band signal with a lowest frequency of 5150 MHz and a highestfrequency of 5170 MHz, the frequency bin of 1 may correspond to 5150 MHzand frequency bin 256 may correspond to 5170 MHz. As another example,128 points of a signal may allow for an FFT with 64 frequency bins.Thus, in a 20 MHz band signal with a lowest frequency of 5150 MHz and ahighest frequency of 5170 MHz, frequency bin 1 may correspond to 5150MHz and frequency bin 64 may correspond to 5170 MHz. In some examples,the lowest frequency bin may not be 1 but it may be any arbitrary number(e.g., 0).

An LTE signal may have characteristics that distinguish it from othersignals that operate in the same unlicensed frequency (e.g., Wi-Fisignal). For example, an LTE signal operating in the unlicensed 5 GHzfrequencies may employ 20 MHz bandwidth as an effort to co-exist withWi-Fi signals operating in close frequencies. Within a 20 MHz bandwidth,LTE uses 18 MHz for data and 2 MHz as guard bands. Guard bands arefrequencies that are unused in the signal in order to prevent the signalfrom interfering with another signal. Thus, a guard band may act as aprotective border or a book-end of a signal. An LTE signal may have oneguard band of 1 MHz at one end of the frequency spectrum in the signal(i.e. the low 1 MHz guard band) and one guard band of 1 MHz at anotherend of the frequency spectrum in the signal (i.e. the high 1 MHz guardband). The location of these guard bands in an FFT and the signalstrength at the locations may be used to help classify a detected signalas being LTE.

Accordingly, instructions 112 may be executable such that processingresource 101 determines a signal strength at a frequency bin in the FFTthat corresponds to a guard band in the signal. This frequency bin maybe characterized as a “guard frequency bin”. Additionally, because anLTE signal has two guard bands, instructions 113 may be executable suchthat processing resource 101 determines a signal strength at a frequencybin corresponding to another guard band. Thus, one guard frequency binmay be characterized as a “first” guard frequency bin and the otherguard frequency bin may be characterized as a “second” guard frequencybin. The signal strength at each may also be characterized as “first”and “second” signal strengths. Thus, the signal strength at the firstguard frequency bin may be characterized as a “first” signal strengthand the signal strength at the second guard frequency bin may becharacterized as a “second” signal strength. Because the guard bands actas a protective border, one guard band is located at the lowestfrequency in an LTE signal (i.e. low guard band) and the other guardband is located at the highest frequency in an LTE signal (i.e. highguard band).

By setting the guard frequency bins at bins that correspond to the guardbands in the signal and determining the signal strength of the FFT atthose set guard frequency bins, signals that do not have a bandwidth of20 MHz may be determined. These signals may be classified as not beingLTE. It is noted that the guard frequency bins are bins that arepredetermined bins. In other words, these bins are set to where theguard bands should be in a 20 MHz signal and may or may not correlate toactual guard bands in the signal being classified. For example, a 40 MHzsignal may not have a guard band at the second guard frequency bin, butit will have a guard frequency bin in its FFT. As another example, a 20MHz signal may have a guard band at the first guard frequency bin and aguard band at the second guard frequency bin.

In some examples, instructions 112 to determine a first signal strengthmay also include instructions to normalize the FFT before determiningthe first signal strength. This may be accomplished by dividing thesignal strength at the first guard frequency bin in the FFT with theEuclidean norm of the FFT. Additionally, instructions 113 to determine asecond signal strength may also include instructions to normalize theFFT before determining the second signal strength. This may beaccomplished by dividing the signal strength at the second guardfrequency bin in the FFT with the Euclidean norm of the FFT. Thenormalization of the FFT may help to reduce noise and inaccuracies inthe FFT. Accordingly, the first signal strength and the second signalstrength determined may be normalized signal strengths.

In some examples, instructions 112 may include instructions to determinethe signal strengths at multiple frequency bins that correspond to thefirst guard band and average those signal strengths together todetermine a signal strength of the first guard band. This is becausemany frequency bins may correspond to the first guard band depending onhow the frequency bins in the FFT are spaced. For example, in an FFTwith 256 samples, the lowest 12 frequency bins may all correspond to thefirst guard band. Thus, in some examples, any one of the lowest 12frequency bins may be individually be used as the first guard frequencybin and the signal strength at that specific frequency bin may be usedas the first signal strength. In other examples, the average of thesignal strengths at these 12 lowest frequency bins may be used as thefirst signal strength. Similarly, instructions 113 may includeinstructions to determine the signal strengths at multiple frequencybins that correspond to the second guard band and average those signalstrengths together to determine a signal strength of the first guardband. For example, in an FFT with 256 samples, the highest 12 frequencybins may all correspond to the second guard band.

Another distinguishing feature in an LTE signal may be the sub-carriersused by LTE. An LTE signal may aggregate a number of orthogonalfrequency division multiplexing (OFDM) sub-carriers together to form thesignal. OFDM may squeeze multiple modulated sub-carriers tightlytogether, reducing the required bandwidth of the signal, but keeping themodulated signals orthogonal so they do not interfere with each other. Asub-carrier in an LTE signal may be a direct current (DC) carrier. In a20 MHz LTE signal, the DC carrier may have a distinct characteristicrelative to other carriers.

Accordingly, instructions 114 may be executable such that processingresource 101 determines a signal strength at a frequency bin thatcorrelates to a DC carrier frequency. This frequency bin may becharacterized as a DC carrier frequency bin. In 20 MHz LTE signals, thefrequency of the DC carrier is at the middle frequency of the bandwidth.For example, in a 20 MHz LTE signal with the lowest frequency of 5030MHz, the DC carrier frequency is at 5040 MHz. Accordingly, in an FFT of256 frequency bins (with frequency bin 1 being the lowest frequencybin), the DC carrier frequency bin is bin 128 As another example, in anFFT of 64 frequency bins, the DC carrier frequency bin is bin 32. Bysetting the DC carrier frequency bin to a bin that corresponds to thefrequency location of the DC carrier and determining the signal strengthof the FFT at that set frequency bin, signals that do not have theexpected characteristic of LTE signal at the DC frequency bin may beclassified as not being LTE. It is noted that the DC frequency bin is apredetermined bin of where the DC carrier should be in a LTE signal andmay or may not correlate to an actual DC carrier in the signal beingclassified. The signal strength at the DC frequency bin may becharacterized as a “third” signal strength relative to the first andsecond signal strength.

In some examples, instructions 114 to determine a first signal strengthmay also include instructions to normalize the FFT before determiningthe third signal strength. This may be accomplished by dividing thesignal strength at the DC carrier frequency bin in the FFT with theEuclidean norm of the FFT.

Instructions 115 may be executable such that processing resource 101classifies the high frequency radio signal based on the first signalstrength, the second signal strength, and the third signal strength.

The signal strengths at the first guard frequency bin and the secondguard frequency bin (the first and second signal strength, respectively)help classify signals that are not 20 MHz, making it less probable thatthe signal is an LTE. For example, in a 20 MHz LTE signal with thelowest frequency of 5030 MHz, the first guard band (the low guard band)may be from 5030-5031 MHz and the second guard band (the high guardband) may be from 5049-5050 MHz. In the FFT of that 20 MHz signal, thelowest frequency bin may correspond to 5030 MHz and the highestfrequency bin may correspond to 5050 MHz. Because these guard bands areunused and thus no information should be sent over them, the amplitudeat the guard frequency bins corresponding to these frequencies should bezero. In some examples, an FFT of a signal having an amplitude higherthan 0 at these guard frequency bins shows that the signal is not a 20MHz signal. For example, it could be a 40 MHz signal, an 80 MHz signal.

Thus, instructions 115 may cause processing resource 101 to determinethat the signal is not LTE based on the first signal strength and/or thesecond signal strength having a signal strength higher than a thresholdof 0. Additionally, instructions 115 may cause processing resource 101to determine that the signal is a 20 MHz signal, and thus more likely tobe LTE, based on the first signal strength and/or the second signalstrength having a strength of 0.

In some examples, the threshold for the guard frequency bins is not 0but is higher to provide an error margin. Additionally, the thresholdmay also depend on the resolution provided by the FFT. A high resolutionFFT may have a lower threshold than a low resolution FFT. Thus, forexample, in an FFT with 256 frequency bins, the threshold may be 0.005while in an FFT with 64 frequency bins, the threshold may be 0.05. Thesenumbers may be the normalized power as discussed above. The thresholdfor the first guard frequency bin and the second guard frequency bin maybe characterized as a guard band threshold. As described herein, asignal strength is considered to be below a threshold if it describes apower that is weaker than the threshold. In terms of normalized power, asignal strength that is arithmetically smaller than the threshold isbelow the threshold (e.g., 0.004 is below a threshold of 0.005). Asignal strength that “meets” the threshold may be equal to or be belowthe threshold.

Additionally, the signal strength at the DC carrier frequency bin (thethird signal strength) further helps to classify signals as being eitherLTE or Wi-Fi. Both LTE and Wi-Fi use OFDM on the PHY layer, withmultiple sub-carriers. With FFT, a frequency resolution that coincideswith the sub-carrier spacing of a signal provides signal strength persub-carrier. Due to the difference between the sub-carrier spacingbetween Wi-Fi and LTE, an FFT of a Wi-Fi signal shows a signal drop atthe DC carrier frequency bin while an FFT of an LTE does not. The signaldrop at the DC carrier frequency bin is relative to adjacent frequencybins. As used herein, a bin is adjacent to another bin if it issequential to a bin. For example, frequency bin 6 is adjacent to bin 7and bin 5. A third signal strength that is lower than the signalstrength at adjacent bins indicates that the signal is Wi-Fi and notLTE. Additionally, the signal strength at the DC carrier frequency binof a WV-Fi signal is lower than the average signal strength of the FFT.In some examples, lower includes at least 70% lower.

In some examples, a third signal strength that is smaller than anaverage signal strength across the frequency bins of the FFT indicatesthat the signal is Wi-Fi and not LTE. Accordingly, in some examples,instructions 115 may include instructions that cause processing resource101 to determine an average signal strength of the FFT. As used herein,an average of the FFT may be calculated by adding the signal strength ateach frequency bin together and dividing that sum by the number offrequency bins.

Thus, instructions 115 may cause processing resource 101 to determinethat the signal is LTE based on a third signal strength being lower thanthe signal strength at adjacent bins and/or lower than the averagesignal strength of the FFT. Additionally, instructions 115 may causeprocessing resource 101 to determine that the signal is a Wi-Fi based ona third signal strength being higher than the signal strength atadjacent bins and/or being higher than the average signal strength ofthe FFT.

In some examples, instructions 115 may cause processing resource 101 totake into account the first and second signal strengths first beforetaking into account the third signal strength. For example, the firstand second signal strengths may be used to filter out signals that arenot LTE. Because LTE uses signals with 20 MHz bandwidths in highfrequencies (and specifically, frequencies in the 5 GHz range), signalsthat are not of 20 MHz bandwidths are not LTE signals. Instructions 115may cause processing resource 101 to discard those signals based on thefirst and second signal strengths and classify them as Wi-Fi. Based on adetermination that the first and second signal strengths indicate that asignal is 20 MHz, instructions 115 may cause processing resource 101 totake into account the third signal strength.

Computing device 100 of FIG. 1, which is described in terms ofprocessors and machine-readable storage mediums, can include one or morestructural or functional aspects of computing device 200 of FIG. 2, orWi-Fi access point 300 of FIG. 3, which is described in terms offunctional engines containing hardware and software.

FIG. 2 is a block diagram of a computing device 200 to classify a highfrequency radio signal. Computing device 200 is similar to computingdevice 100. Computing device 200 includes a processing resource 201 anda machine-readable storage medium 210. Processing resource 201 issimilar to processing resource 101 and machine-readable storage medium210 is similar to machine-readable storage medium 110. Instructions 211,212, 213, 214, 215, and 216 are stored (encoded) on storage medium 210and are executable by processing resource 201 to implementfunctionalities described herein in relation to FIG. 2.

Instructions 211 may be executable by processing resource 201 to receivea FFT of a high frequency radio signal. In some examples, the highfrequency radio signal may be a 5 GHz radio signal. Instructions 211 aresimilar to instructions 111 and the discussion above in relation toinstructions 111 is applicable here.

Instructions 212 may be executable by processing resource 201 todetermine a maximum strength of the FFT. As used herein, a maximumstrength includes the highest signal strength of the FFT. This may becharacterized as a global peak of the FFT or a maxima of the FFT. Insome examples, instructions 212 may accomplish this by looking throughthe amplitudes of the FFT and marking the highest signal reading as themaximum strength. Some signals are not strong enough to be a cause ofinterference. As discussed in relation to instructions 214, computingdevice 200 may use this maximum strength of the FFT to filter outsignals that are not interfering.

Instructions 213 may be executable by processing resource 201 todetermine a number of peaks in the FFT that are above a threshold. Asused herein, peaks in the FFT includes frequency bins in which thesignal strength at adjacent bins on the both sides of the frequency binis lower than the signal strength at the frequency bin. For example, thesignal strength at frequency bin 100 may be −100 dBm, the signalstrength at frequency bin 101 may be −80 dBm, and the signal strength offrequency bin 102 may be −100 dBm. This would indicate that there is a“peak” at frequency bin 101 of −80 dBm. As another example, the signalstrength at frequency bin 104 may be −85 dBm, the signal strength atfrequency bin 105 may be −67 dBm, and the signal strength of frequencybin 106 may be −50 dBm. This would indicate that there is no peakamongst frequency bins 104, 105, and 106. These peaks may becharacterized as local peaks. The global peak (as discussed in relationto instructions 212) may also be a local peak. As used herein, a numbermay include any number including 0, 1, 2, 3, etc. In other words,instructions 213 may determine how many, if any, peaks there are in theFFT that are above a specific threshold.

The threshold may be set where, above that signal strength, a signal isconsidered to be interfering. As discussed above, an FFT may havedifferent number of frequency bins. A higher number of frequency binsprovide a higher resolution of the signal. A lower number of frequencybins provide a lower resolution of the signal. In some examples, thespecific threshold may depend on the resolution of the FFT. According toParseval's Theorem, the total energy of a signal is the same for any FFTresolution. Thus, as the resolution of the FFT increases, the signalstrength at each frequency bin may decrease. In some examples, where theFFT has 256 frequency bins, the threshold may be −89 dBm. In anotherexamples, where the FFT has 64 frequency bins, the threshold may be −85dBm.

As discussed above, LTE signals are OFDM. A signal that is OFDM mayinclude multiple peaks that are at or above the specific threshold.Accordingly, as discussed in relation to instructions 214, computingdevice 200 may use the number of peaks in the FFT to help filter outsignals that are not OFDM and thus, not LTE.

Instructions 214 may be executable by processing resource 201 todetermine a signal strength at a first guard frequency bin and a secondsignal strength at a second guard frequency bin. This determination maybe in response to a determination that the maximum strength (asdetermined by instructions 212) exceeds a strength threshold and thenumber (as determined by instructions 213) exceeds a number threshold.

The strength threshold may be the same as the threshold used ininstructions 214 to determine which peak to count in “the number.”Accordingly, in some examples, where the FFT has 256 frequency bins, thestrength threshold may be −89 dBm. Additionally, in other examples,where the FFT has 64 frequency bins, the strength threshold may be −85dBm. A signal strength is considered to exceed a threshold if itdescribes a signal strength (i.e. power) that is stronger than thethreshold. In terms of dBM units, a smaller negative number (e.g. −30dBm) is stronger than a bigger negative number (−90 dBm).

The number threshold may be a number that, when the number of peaks isabove this number, indicates that the signal is an OFDM signal. In someexamples, the number threshold may be 10. In some examples, the numberthreshold may be dependent on the FFT sample received and may be varieddependent on factors such as FFT resolution, etc. For example, an OFDMsignal being represented by a higher resolution FFT may have more peaksas compared an OFDM signal that is being represented by a lowerresolution FFT. In some examples, the number may be changed and adaptedbased on the individual characteristics of the equipment being used toprovide the FFT using machine learning. In some examples, machinelearning may include first baseline of rules for a computing device tofollow, allowing the computing device to make determinations based onthose rules, and verifying the determinations of the computing device,and modifying the rules if needed.

Thus, instructions 212 may cause processing resource 201 to determinethat an FFT with 256 frequency bins has a maximum strength of −67 dBM.Additionally, instructions 213 may cause processing resource 101 todetermine that an FFT with 256 frequency bins has 11 peaks (each peakhas a strength of at least −85 dBm). Instructions 214 may compare themaximum strength to the strength threshold and determine that it exceedsthe threshold. Instructions 214 may also compare the number of peaks tothe number threshold and determine that it exceeds the threshold. Basedon these determinations, instructions 214 may cause processing resource101 to determine a signal strength at a first guard frequency bin and asecond signal strength at a second guard frequency bin. However, basedon a determination that an FFT does not have a maximum strengthexceeding the strength threshold, instructions 214 may cause processingresource 101 to determine that the signal is not an interfering signaland ignore the signal. Additionally, based on a determination that anFFT has 10 peaks, instructions 214 may cause processing resource 201 todetermine that the signal is not an OFDM signal and thus not LTE. Insome examples, the strength threshold may be characterized as a firstthreshold and the number threshold may be characterized as a secondthreshold as a mechanism to discriminate between the thresholds.

The first signal strength, the second signal strength, the first guardfrequency bin, and the second guard frequency bin are similar to thefirst signal strength, the second signal strength, the first guardfrequency bin, and the second guard frequency bin, respectively, asdiscussed in relation to instructions 111, 112, and 113. Additionally,as discussed above, a normalization of power of an FFT may help toalleviate inaccuracies in the sampling. As such, instructions 214 mayalso include instructions executable by processing resource 101 tonormalize the FFT in response to a determination that the maximumstrength exceeds the first threshold and a determination that the numberexceeds a second threshold. Accordingly, the maximum strength and thenumber of peaks (in instructions 212 and 213) are determined on the FFTand the first signal strength and the second signal strength aredetermined on the normalized FFT.

Instructions 215 may be executable by processing resource 201 todetermine a third signal strength at a direct current carrier frequencybin. This determination may be in response to a determination that thefirst signal strength and the second signal strength (in instructions214) meet a guard band threshold. The third signal strength is similarto the third signal strength described above in relation to instructions114. The DC carrier frequency bin is similar to the DC carrier frequencybin described above in relation to instructions 114. The guard bandthreshold is similar to the guard band threshold described above inrelation to instructions 115

Thus, instructions 214 may cause processing resource 201 to determinethat an FFT with 256 frequency bins has a first signal strength of 0.005and a second signal strength of 0.004. Instructions 215 may causeprocessing resource to determine that these signal strengths meet thethreshold of 0.005. In response to this determination, instructions 215may cause processing resource 101 to determine a third signal strengthat the DC carrier frequency bin. However, based on a determination thatthe FFT has a first signal strength higher than 0.005 (e.g., 0.0055,0.006, etc.), instructions 215 may cause processing resource 101 todetermine that the signal is not 20 MHz and classify the signal asWi-Fi.

Instructions 216 may be executable by processing resource 201 toclassify the radio frequency signal based on the third signal strength.This is similar to the third signal strength described above in relationto instructions 115.

As discussed above, an FFT may have different number of frequency bins.A higher number of frequency bins provide a higher resolution of thesignal. A lower number of frequency bins provide a lower resolution ofthe signal. Thus, the signal strength readings may depend on theresolution of the signal (i.e. the number of frequency bins). In a highresolution FFT, more readings of additional frequency bins may beprovided.

Thus, in some examples, in a high resolution FFT, instructions 216 maybe executable by processing resource 201 to classify based on the thirdsignal strength (at the DC frequency bin), and signal strengths at twoadditional frequency bins. The first additional frequency bin maycorrelate to the low guard band of the signal (as described above) andthe second additional frequency bin may correlate to the high guard bandof the signal (as described above).

These additional frequency bins are used because LTE technology employsa certain amount of sub-carriers when operating in a specific bandwidth.For example, on a 20 MHz bandwidth, LTE uses 2048 sub-carriers, with a15 KHz sub-carrier spacing. This leaves 2 MHz for guard bands, asdiscussed above. Wi-Fi, on the other hand, provisions for 64sub-carries, with a sub-carrier spacing of 312.5 KHz. This provides atotal used bandwidth of 17.8 MHz and 2.2 MHz used as guard bands. Thus,the difference in the guard bands of the two signals differ in 0.2 MHz(0.1 MHz on each border of the signal). Accordingly, the guard bands fora Wi-Fi signal may span across a wider frequency range than the guardbands used for LTE.

Thus, the additional frequency bin for the low guard band may be locatedat a frequency bin that correlates to the highest frequency of the lowguard band for an expected 20 MHz Wi-Fi signal. For example, a low guardband of a 20 MHz signal beginning at 5030 MHz starts at 5030 MHz. In anLTE signal, the low guard band may be from 5030-5031 MHz. In a Wi-Fisignal, the low guard band may be from 5030-5031.1 MHz. Thus, theadditional frequency bin for the low guard band may correlate to 5031.1MHz. This additional frequency bin may be characterized as a third guardfrequency bin. Because this additional frequency bin is correlated tothe low guard band, this third frequency bin is lower than the DCfrequency bin. In some examples, this frequency bin may be determined by14×N/256, where N is the frequency bins in the FFT. Thus, in an FFT with256 frequency bins (N=256), this frequency bin may be located at bin 14.The signal strength at this additional frequency bin may becharacterized as a fourth signal strength.

Similarly, the additional frequency bin correlated to the high guardband may be located at a frequency bin that correlates to the lowestfrequency of the high guard band for an expected 20 MHz Wi-Fi signal.For example, a high guard band of a 20 MHz signal beginning at 5030starts at 5049 MHz. In an LTE signal, the low guard band may be from5030-5031 MHz. In a WV-Fi signal, the low guard band may be from5030-5031.1 MHz. Thus, the additional frequency bin for the low guardband may correlate to 5031.1 MHz. This additional frequency bin may becharacterized as a fourth frequency bin. Because this additionalfrequency bin is correlated to the high guard band, this fourthfrequency bin is higher than the DC frequency bin. In some examples,this frequency bin may be determined by 244×N/256, where N is thefrequency bins in the FFT. Thus, in an FFT with 256 frequency bins(N=256), this frequency bin may be located at bin 244. The signalstrength at this additional frequency bin may be characterized as afifth signal strength.

The classification of the signal may be based on the third signalstrength (at the DC carrier frequency bin) and the fourth signalstrength (at the low guard band). Based on the determination that thethird signal strength is below a threshold (i.e. the DC carrierthreshold), instructions 216 on storage medium 210 may cause processingresource 201 to further look at the fourth signal strength. Based on adetermination that the fourth signal strength is below another threshold(i.e. low guard band threshold), instructions on storage medium 210 maycause processing resource 201 to classify the signal as a Wi-Fi signal.Based on a determination that the fourth signal strength is at orexceeds the low guard band threshold, instructions on storage medium 210may cause processing resource 201 to classify the signal as LTE signal.

Thus, when the third signal strength is below the DC carrier threshold,the classification of the signal may be based on the third signalstrength and the fourth signal strength. However, based on adetermination that the third signal strength is at or exceeds the DCcarrier threshold, instructions on storage medium 210 may causeprocessing resource 201 to further look at the fifth signal strength (atthe high guard band) instead of the fourth signal strength. Based on adetermination that the fifth signal strength is below another threshold(high guard band threshold), instructions on storage medium 210 maycause processing resource 201 to classify the signal as a Wi-Fi signal.Based on a determination that the fifth signal strength is at or exceedsthe high guard band threshold, instructions on storage medium 210 maycause processing resource 201 to classify the signal as LTE signal.

In some examples, the DC carrier threshold may be 0.039. In someexamples, the low guard threshold may be 0.010. In some examples, thehigh guard threshold may be 0.019. In some examples, these thresholdsmay be changed and adapted based on the individual characteristics ofthe equipment being used to provide the FFT using machine learning. Insome examples, machine learning may include providing a baseline ofrules for a computing device to follow, allowing the computing device tomake determinations based on those rules, verifying the determinationsof the computing device, and modifying the rules if needed.

In an FFT providing a low resolution, such as an FFT with 64 frequencybins, it may not be possible to determine the fourth signal strength andthe fifth signal strength that correspond to the low guard band and thehigh guard band due to the low resolution. Thus, in a low resolutionFFT, storage medium 201 may include instructions that are executable tocause processing resource 201 to look at other characteristics of aWi-Fi signal. These instructions may programmed such that they areexecuted before the execution of 214, 215, and 216. These instructionsmay thus help to filter out the amount of signals that may be processedby 214, 215, and 216. Accordingly, these instructions may be executed byprocessing resource 201 on the FFT and not a normalized FFT.

The instructions may be executable by processing resource 201 todetermine whether peaks exist at pre-determined frequency bins. Thesepre-determined frequency bins may correlate to the legacy short trainingfield (L-STF) in a Wi-Fi signal. The L-STF signal is a signal that istransmitted by Wi-Fi before it starts its data transmissions. In anL-STF, there are signal peaks that occur at 12 known frequencies. Asignal transmitted by Wi-Fi has a legacy short training field signal anda signal transmitted by LTE does not. Thus, instructions on storagemedium 201 may cause processing resource 210 to determine the signalstrengths at frequency bins that correspond to the frequencies known tohave peaks in an L-STF. These frequency bins may be characterized asL-STF frequency bins. In some examples, these frequency bins may bedefined by the Wi-Fi community (e.g., IEEE 802.11 standard). In someexample, the signal strengths are determined to determine whether thereare peaks existing in the signal at the L-STF frequency bins. Thus, insome examples, the signal strength at L-STF frequency bins relative tothe signal strengths at the adjacent bins may help to classify thesignal.

A peak may be determined by looking at the signal strengths of adjacentbins of the L-STF frequency bin. If the signal strengths at binsadjacent to the L-STF frequency bin are lower than the signal strengthat an L-STF frequency bin, then there is a peak at that specific L-STFbin. If the signal strengths at adjacent bins are higher or equal to thesignal strength at an L-STF bin, then there is not a peak at that L-STFbin. Based on a determination that there are 12 peaks, each at an L-STFfrequency bin, instructions are executable by processing resource 201 toclassify that signal as Wi-Fi. A signal that is classified as beingWi-Fi may not go through further analyzation (i.e., instructions 214,215, and 216). Based on a determination that there are not 12 peaks atthe L-STF frequency bins, instructions are executable by processingresource 201 to determine a first signal strength at a first guardfrequency bin and a second signal strength at a second guard frequencybin, as described above in relation to instructions 214. Accordingly,the peaks at L-STF frequency bins may be determined before the FFT isnormalized. In some examples, a signal with at least 8 peaks (one peakat at least 8 out of 12 of the L-STF frequency bins) may be classifiedas a Wi-Fi signal. This allows for sampling error.

Thus, accordingly, in some examples, instructions stored on storagemedium 210 may include instructions to determine what resolution isprovided by the FFT. Based on a determination that the resolutionprovided by the FFT is high (at least 100 KHz, e.g., 100 KHz, 90 KHz, 80KHz, etc.), instructions on storage medium 210 may determine anadditional signal strength at an additional frequency bin correlated tothe low guard band and an additional signal strength at an additionalfrequency bin correlated to the high guard band. Based on adetermination that the resolution provided by the FFT is low (higherthan 100 KHz, e.g. 110 KHz, 120 KHz), instructions on storage medium 210may determine a signal strengths at the L-STF frequency bins.

Computing device 200 of FIG. 2, which is described in terms ofprocessors and machine-readable storage mediums, can include one or morestructural or functional aspects of computing device 100 of FIG. 1, orWi-Fi access point 300 of FIG. 3, which is described in terms offunctional engines containing hardware and software. For example,computing device 200 may have instructions to implement thefunctionalities of normalization engine 302 as described in relation toFIG. 3.

FIG. 3 illustrates a block diagram of a Wi-Fi access point 300. In someexamples, access point 300 may connect to a wired router/switch/hub viaan Ethernet cable and project a Wi-Fi signal to a designated area,creating a wireless local area network (WLAN). Wi-Fi access point 300includes an FFT engine 301, a normalization engine 302, and aclassification engine 303. Each of these aspects of Wi-Fi access point301 will be described below. Other engines can be added to Wi-Fi accesspoint 301 for additional or alternative functionality.

Each of engines 301, 302, 303, and any other engines, may be anycombination of hardware (e.g., a processor such as an integrated circuitor other circuitry) and software (e.g., machine or processor-executableinstructions, commands, or code such as firmware, programming, or objectcode) to implement the functionalities of the respective engine. Suchcombinations of hardware and programming may be implemented in a numberof different ways. A combination of hardware and software can includehardware (i.e., a hardware element with no software elements), softwarehosted at hardware (e.g., software that is stored at a memory andexecuted or interpreted at a processor), or hardware and software hostedat hardware. Additionally, as used herein, the singular forms “a,” “an,”and “the” include plural referents unless the context dearly dictatesotherwise. Thus, for example, the term “engine” is intended to mean atleast one engine or a combination of engines. In some examples, Wi-Fiaccess point 300 may include additional engines.

Each engine of Wi-Fi access point 300 can include at least onemachine-readable storage mediums (for example, more than one) and atleast one computer processor (for example, more than one). For example,software that provides the functionality of engines on Wi-Fi accesspoint 300 can be stored on a memory of a computer to be executed by aprocessor of the computer.

FFT engine 301 is an engine of Wi-Fi access point that includes acombination of hardware and software that allows Wi-Fi access point toreceive an FFT of a signal. As discussed above, the signal may be a highfrequency radio signal. In some examples, the high frequency radiosignal may be a channel in a specific frequency range. For example, thesignal may be transmitted on channel 7 in the 5 GHz frequency range. Asanother example, the signal may be transmitted on channel 50 in the 5GHz frequency range. FFT engine 301 may implement the functionalities asdescribed in relation to instructions 211. In some examples, FFT engine301 allows Wi-Fi access point 300 to receive multiple FFTs of the samesignal (e.g., a first FFT, a second FFT, a third FFT). In some examples,these FFTs may be of the same resolution as each other.

Normalization engine 302 is an engine of Wi-Fi access point 300 thatincludes a combination of hardware and software that allows Wi-Fi accesspoint 300 to determine a maximum strength of the FFT. Normalizationengine 302 also allows Wi-Fi access point 300 to determine a number ofpeaks in the FFT that exceeds a first threshold. Accordingly,normalization engine 302 may implement the functionalities as describedin relation to instructions 212 and 213. As discussed above, FFT engine301 may receive multiple FFTs of the same signal. Accordingly,normalization engine 302 may determine the maximum strength of each FFTand determine a number of peaks in each FFT. Normalization engine 302may then normalize each FFT and average the FFTs based on adetermination that the FFTs within a certain time period meet thecriteria of maximum threshold and peak numbers. For example, the timeperiod may be set at 1 microsecond. FFT engine 301 may receive FFTs ofthe signal for 1 microsecond. Normalization engine 302 may determine themaximum strength of each FFT received in the microsecond. Normalizationengine 302 may also determine the number of peaks of each FFT receivedin the microsecond. Based on a determination that a certain percentageof FFTs received in the microsecond has: 1) a maximum strength exceedingthe strength threshold, and 2) a number of peaks exceeding the numberthreshold, normalization engine 302 may normalize each FFT and averageall the FFTs to determine an average FFT to represent the FFTs receivedin that time period. The percentage may be 100% (e.g., all FFTs receivedin the microsecond), or a majority (51%), etc. Based on a determinationthat a certain percentage of FFTs received in the microsecond does notmeet condition 1 and/or 2, then the time period starts over and resets.

Classification engine 303 is an engine of Wi-Fi access point 300 thatincludes a combination of hardware and software that allows Wi-Fi accesspoint 300 to determine a first signal strength at a first guardfrequency bin and a second signal strength at a second guard frequencybin. In some examples, the determination may be made on the average FFTas determined by normalization engine 302. Classification engine 303 mayalso allow Wi-Fi access point 300 to determine a third signal strengthat a DC carrier frequency bin based on a determination that the firstsignal strength and the second signal strength meet a third threshold.Additionally, classification engine 303 may classify the radio frequencysignal based on the third signal strength. Thus, classification engine303 may implement the functionalities as described in relation toinstructions 214, 215, and 216.

In some examples, FFT engine 301 may determine whether the FFTs are alow resolution FFTs or a high resolution FFTs. This determination mayaffect normalization engine 302 and classification engine 303. Based ona determination that the FFTs received provide low resolution,normalization engine 302 may look at the signal strengths at the L-STFfrequency bins of the FFTs received within the preset time period. Basedon a determination that a certain percentage of the FFTs do not havepeaks at the L-STF frequency bins (and meet the peak threshold andnumber threshold, as discussed above), normalization engine 302 maynormalize and average the FFTs as discussed above. Based on adetermination that the FFTs received provide high resolution,normalization engine 302 does not look at the L-STF frequency bins.

Based on the determination of FFT engine 301 that the FFTs receivedprovide high resolution, classification engine 303 may determine afourth signal strength at a third guard frequency bin and a fifth signalstrength at a fourth guard frequency bin, as discussed above in order tohelp classify the signal. The fourth signal strength and the fifthsignal strength may be based on the average FFT determined bynormalization engine 302.

Wi-Fi access point 300 of FIG. 3, which is described in terms offunctional engines containing hardware and software, can include one ormore structural or functional aspects of computing device 100 of FIG. 1,or computing device 200 of FIG. 2, which is described in terms ofprocessors and machine-readable storage mediums.

FIG. 4 shows an FFT of a 20 MHz LTE signal (which is depicted by a grayline) and an FFT of a 20 MHz Wi-Fi signal (which is depicted by a blackline), both with 256 frequency bins. Both FFTs have been normalized.Accordingly, the unit for the x-axis is frequency bins and the unit forthe y-axis is normalized power. 400A marks a low guard band area and400B marks a high guard band area. Because the LTE signal and the Wi-Fisignal are both 20 MHz, both FFTs have low normalized power in areas400A and 400B. 400C marks a DC carrier area. As shown by FIG. 4, theWi-Fi FFT has a power drop at that area and the LTE FFT does not.Accordingly, this area may be used to help distinguish the LTE FFT fromthe WV-Fi FFT.

400D marks an additional frequency bin area correlated with the lowguard band area and 400E marks an additional frequency bin areacorrelated with the high guard band area. 401D shows a close-up of 400D.401E shows a close-up of 400E.

As shown by 401D, the low guard band of the Wi-Fi signal spans acrossmore frequency bins than the low guard band of the LTE signal.Similarly, as shown by 401E, the high guard band of the Wi-Fi signalspans across more frequency bins than the high guard band of the LTEsignal. Accordingly, these areas may be used to help distinguish the LTEFFT from the WV-Fi FFT.

FIG. 5 illustrates a flowchart for a method 500 to classify a highfrequency radio signal. Although execution of method 500 is describedbelow with reference to Wi-Fi access point 300 of FIG. 3, other suitabledevices for execution of method 300 can be utilized (e.g., computingdevice 100 of FIG. 1 or computing device 200 of FIG. 2). Additionally,implementation of method 500 is not limited to such examples and can beused for any suitable devices or system described herein or otherwise.

At 510 of method 500, FFT engine 301 receives a first FFT of a highfrequency radio signal. As discussed above, the high frequency radiosignal may be on a specific channel in the 5 GHz range. At 520 of method500, normalization engine 302 determines a first maximum strength of thefirst FFT. At 530, normalization engine 302 determines a first number ofpeaks in the first FFT that are above a first threshold. As describedabove, the first threshold may be a strength threshold. In someexamples, for a 5 GHz signal, the threshold may be −85 dBm. At 540, FFTengine 301 receives a second FFT of the high frequency radio signal. At550, normalization engine 302 may determine a second maximum strength ofthe second FFT. At 560, normalization engine 560 may determine a secondnumber of peaks in the second FFT that are above the first threshold. At570, normalization engine 302 may determine an average FFT based on thefirst FFT and the second FFT. 570 may be in response to a determinationthe first maximum and the second maximum both meet the first thresholdand a determination that the first number and the second number bothmeet a second threshold. In some examples, normalization engine 302 maynormalize the first FFT and normalize the second FFT before averagingthe first FFT and the second FFT to get an average FFT.

At 580, classification engine 303 may classify the high frequency radiosignal based on the signal strength of the average FFT at a first guardfrequency bin, a signal strength of the average FFT at a second guardfrequency bin, and a signal strength of the average FFT at a DC carrierfrequency bin. First guard frequency bin, second guard frequency bin,and DC carrier frequency bin are similar to those discussed above inrelation to FIG. 1.

Although the flowchart of FIG. 5 shows a specific order of performanceof certain functionalities, method 500 is not limited to that order. Forexample, some of the functionalities shown in succession in theflowchart may be performed in a different order, may be executedconcurrently or with partial concurrence, or a combination thereof. Insome examples, 540 may be started before 520 is completed. Additionally,while FIG. 5 specifically mentions a first FFT and a second FFT, theremay be additional FFTs that are received (e.g., 8 additional FFTs). Forexample, a third FFT may be received and analyzed before 570. 570 isthen performed in response to the additional FFTs also having a maximumstrength above the first threshold and a number of peaks that is abovethe second threshold. The average determined in 570 is then based on thefirst FFT, the second FFT, and any additional FFTs.

FIG. 6 is a flowchart of a method of classifying a high frequency radiosignal using a high resolution FFT. Although execution of method 600 isdescribed below with reference to Wi-Fi access point 300 of FIG. 3,other suitable devices for execution of method 600 can be utilized(e.g., computing device 100 of FIG. 1 or computing device 200 of FIG.2). Additionally, implementation of method 600 is not limited to suchexamples and can be used for any suitable devices or system describedherein or otherwise.

At 610, FFT engine 301 receives FFTs of a high frequency radio signalover a predetermined time period. As discussed above, this predeterminedtime period may be for 1 microsecond. The FFTs received may provide ahigh resolution of the radio signal. At 620, normalization engine 302determines the maximum strengths of each of the FFTs received at 610. At630, normalization engine 302 determines a number of peaks for each FFTthat are above a first threshold. Accordingly, each FFT will have anumber that identifies how many peaks each FFT has that are above thefirst threshold. As discussed above, this first threshold may be astrength threshold. At 671, normalization engine 302 determines whetherthe maximum strength of each FFT is above the first threshold. Thisfirst threshold is the same threshold used in 630. Based on adetermination that each FFT received in the predetermined time periodhas a maximum strength that is above the first threshold, methodproceeds to 672. Based on a determination that at least one FFT (out ofall the FFT received in the predetermined time period at 610) has amaximum strength that meets (i.e. is equal or is below) the firstthreshold, method moves back to 610 to receive new FFTs. The old FFTsare discarded.

Referring back to 672, normalization engine 302 determines if the numberof peaks of each FFT are above a second threshold. As discussed above inrelation to instructions 214, this second threshold may be the numberthreshold and indicate that the signal is an OFDM signal. In otherwords, at 672, normalization engine 302 determines if each FFT receivedin the predetermined time period has enough peaks. Based on adetermination that each FFT has enough peaks, method proceeds to 673.Based on a determination that at least one FFT (out of the FFTs receivedin the predetermined time period at 610) has a number of peaks thatmeets (equal to or is below) the second threshold, method moves back to610 to receive new FFTs. The old FFTs are discarded.

Referring back to 673, normalization engine 302 normalizes each FFTreceived in the predetermined period and then averages the normalizedFFTs to get an average FFT. At 681, classification engine 303 determinesa signal strength at a highest frequency bin of the average FFT and asignal strength at the lowest frequency bin of the average FFT. Thehighest frequency bin may correspond to a high guard band of the signaland the lowest frequency bin may correspond to a low guard band of thesignal. In other examples, and as described above in relation toinstructions 112 and 113, classification engine 303 may determine asignal strength at all of the frequency bins that correspond to the lowguard band in the average FFT (the 12 lowest frequency bins) and averagethose signal strengths to determine a signal strength for the low guardband. Additionally, classification engine 303 may determine a signalstrength at all of the frequency bins that correspond to the high guardband in the average FFT (the 12 highest frequency bins) and averagethose signal strengths to determine a signal strength for the high guardband. Those signal strengths may then be used at 682.

At 682, classification engine 303 determines if the signal strengthsdetermined at 681 exceeds a third threshold. This third threshold may bea guard band threshold, as discussed above. Based on a determinationthat either signal strengths exceeds the third threshold, method returnsback to 610 to receive new FFTs. The old FFTs are discarded. This isbecause this indicates that the signal is not 20 MHz and thus cannot beLTE operating in a high frequency.

Based on a determination that both signal strengths meets (equal to orbelow) the third threshold, method moves to 683. At 683, classificationengine 303 determines a signal strength at a DC carrier frequency bin ofthe average FFT. At 684, classification engine 303 determines whetherthe signal strength at the DC carrier frequency bin is below a fourththreshold. The fourth threshold may be the DC carrier threshold (0.039),as discussed above. Based on a determination that the signal strength(determined at 683) is equal to or exceeds the fourth threshold, methodproceeds to 685. Based on a determination that the signal strength(determined at 683) is below the fourth threshold, method proceeds to689.

At 685, classification engine 303 looks at an additional frequency bincorrelated to the low guard band of the signal. This may becharacterized as a third guard frequency bin. In some examples, thisguard frequency bin may be defined as 14×N/256, where N is the number offrequency bins in the average FFT. At 686, classification engine 303determines whether the signal strength (determined at 685) is equal toor above a fifth threshold. This fifth threshold is the low guard bandthreshold, as discussed above. In some examples, this fifth threshold is0.010. Based on a determination that the signal strength determined at685 is equal to or above the fifth threshold, method 600 proceeds to687, where classification engine 303 classifies the signal as an LTEsignal. Based on a determination that the signal strength determined at685 is below the fifth threshold, method 600 proceeds to 688, whereclassification engine 303 classifies the signal as a WV-Fi signal.

Referring back to 684, based on a determination that the signal strength(determined at 683) is below the fourth threshold (i.e. DC carrierthreshold), method proceeds to 689. At 689, classification engine 303looks at an additional frequency bin correlated to the high guard bandof the signal. This may also be characterized as a third guard frequencybin. In some examples, this guard frequency bin may be defined as244×N/256, where N is the number of frequency bins in the average FFT.At 690, classification engine 303 determines whether the signal strength(determined at 689) is equal to or above a fifth threshold. The fifththreshold, in this context, is the high guard band threshold. In someexamples, the fifth threshold is 0.019. Based on a determination that itis equal to or above the fifth threshold, method 600 proceeds to 692,where classification engine 303 classifies the signal as an LTE signal.Based on a determination that it is below the fifth threshold, method600 proceeds to 691, where classification engine 303 classifies thesignal as a Wi-Fi signal.

Although the flowchart of FIG. 6 shows a specific order of performanceof certain functionalities, method 600 is not limited to that order. Forexample, some of the functionalities shown in succession in theflowchart may be performed in a different order, may be executedconcurrently or with partial concurrence, or a combination thereof.

FIG. 7 is a flowchart of a method of classifying a high frequency radiosignal using a low resolution FFT. Although execution of method 700 isdescribed below with reference to Wi-Fi access point 300 of FIG. 3,other suitable devices for execution of method 700 can be utilized(e.g., computing device 100 of FIG. 1 or computing device 200 of FIG.2). Additionally, implementation of method 600 is not limited to suchexamples and can be used for any suitable devices or system describedherein or otherwise.

710, 720, 730, 771, and 772 are similar to 610, 620, 630, 671, and 672,respectively, except that the resolution provided by FFTs in method 700is a low resolution.

Because the FFTs provide low resolution, at 773, normalization engine302 may determine signal strengths at frequency bins correlated with thelegacy short training field (L-STF) in each FFT received at 710. Thisallows Wi-Fi access point 300 to filter out signals that are Wi-Fi. At774, normalization engine 300 determines whether each FFT has peaks atthe L-STF frequency bins. Based on a determination that each FFT has atleast 8 peaks (for at least 8 out of the 12 L-STF frequency bins),method proceeds to 781, where classification engine 303 classifies thesignal as a Wi-Fi signal.

Based on a determination that at least one FFT (received at 710) doesnot have the peaks at the L-STF frequency bin (e.g. one FFT has only 7peaks at 7 out of the 12 L-STFT frequency bins), method proceeds to 775.At 775, normalization engine normalizes each FFT received in thepredetermined period and then averages the normalized FFTs to get anaverage FFT.

782 of method 700 is similar to 681 of method 600. 783 of method 700 issimilar to 682 of method 600, except that in an FFT with 64 frequencybins, the 3 lowest frequency bins all correspond to the low guard bandand the 3 highest frequency bins all correspond to the high guard band.784 of method 700 is similar to 683 of method 600. At 785,classification engine 303 determines whether there is a signal strengthdrop at the DC carrier frequency bin (determined at 784) relative toadjacent bins of the direct current carrier frequency bins. Adjacentbins, as described above, are applicable here. Based on a determinationthat there is not a signal drop with respect to adjacent bins, methodproceeds to 787, where classification engine 303 classifies the signalas an LTE signal. Based on a determination that there is a signalstrength drop with respect to adjacent bins, method proceeds to 786,where classification engine 303 classifies the signal as a Wi-Fi signal.

Although the flowchart of FIG. 7 shows a specific order of performanceof certain functionalities, method 700 is not limited to that order. Forexample, some of the functionalities shown in succession in theflowchart may be performed in a different order, may be executedconcurrently or with partial concurrence, or a combination thereof.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the elementsof any method or process so disclosed, may be combined in anycombination, except combinations where at least some of such featuresand/or elements are mutually exclusive.

What is claimed is:
 1. A non-transitory machine-readable storage mediumcomprising instructions, that, when executed, cause a processingresource to: receive a fast Fourier transform (FFT) of a high frequencyradio signal, wherein the FFT comprises a direct current (DC) carrierfrequency bin, a first guard frequency bin lower than the DC carrierfrequency bin, and a second guard frequency bin higher than the DCcarrier frequency bin; determine a first signal strength at the firstguard frequency bin; determine a second signal strength at the secondguard frequency bin; determine a third signal strength at the DC carrierfrequency bin; and classify the high frequency radio signal based on thefirst signal strength, the second signal strength, and the third signalstrength.
 2. The storage medium of claim 1, wherein the signal isclassified as Long Term Evolution (LTE) based on the first signalstrength meeting a guard band threshold, the second signal strengthmeeting the guard band threshold, and the third signal strength beingbelow a DC threshold.
 3. The storage medium of claim 1, wherein the FFTprovides a low resolution of the signal; wherein the FFT compriseslegacy short training field (L-STF) frequency bins; and wherein theclassification is based on signal strengths at the L-STF frequency bins.4. The storage medium of claim 1, wherein the high frequency radiosignal comprises a 5 GHz signal; wherein the first guard frequency bincorresponds to a low 1 MHz guard band in the signal; and wherein thesecond guard frequency bin corresponds to a high 1 MHz guard band in thesignal.
 5. The storage medium of claim 1, wherein the high frequencyradio signal comprises a 5 GHz signal; wherein the FFT provides aresolution of at least 100 KHz; and wherein the classification is basedon a fourth signal strength at a third guard frequency bin that is lowerthan the DC carrier frequency bin.
 6. The storage medium of claim 5,wherein the first guard frequency bin is associated with a beginning ofa guard band in the signal and the third guard frequency bin isassociated with an end of the guard band.
 7. The storage medium of claim1, wherein the high frequency radio signal comprises a 5 GHz signal;wherein the FFT provides a resolution of at least 100 KHz; and whereinthe classification is based on a fourth signal strength at a third guardfrequency bin that is higher than the DC carrier frequency bin.
 8. Thestorage medium of claim 7, wherein the second guard frequency bin isassociated with a beginning of a guard band in the signal and the thirdguard frequency bin is associated with an end of the guard band.
 9. Thestorage medium of claim 1, wherein the FFT comprises a maximum signalstrength; and wherein the classification is based on the maximum signalstrength exceeding a strength threshold.
 10. The storage medium of claim1, wherein the FFT comprises a number of peaks that exceed a strengththreshold; and wherein the classification is based on the number ofpeaks.
 11. A non-transitory machine-readable storage medium comprisinginstructions, that, when executed, cause a processing resource to:receive an FFT of a high frequency radio signal; determine a maximumstrength of the FFT; determine a number of peaks in the FFT that exceedsa first threshold; in response to a determination that the maximumstrength exceeds the first threshold and a determination that the numberexceeds a second threshold, determine a first signal strength at a firstguard frequency bin and a second signal strength at a second guardfrequency bin; in response to a determination that the first signalstrength and the second signal strength meet a third threshold,determine a third signal strength at a direct current (DC) carrierfrequency bin; and classify the high frequency radio signal based on thethird signal strength.
 12. The storage medium of claim 11, wherein thesignal is classified as LTE based on the third signal strength beingabove a threshold.
 13. The storage medium of claim 11, wherein the highfrequency radio signal comprises a 5 GHz signal; wherein the FFTcomprises a resolution of at least 100 KHz; wherein the storage mediumcomprises instructions, that, when executed, cause the processingresource to determine a fourth signal strength at a third guardfrequency bin that is lower than the direct currency frequency bin; andwherein the classification is based on the fourth signal strength. 14.The storage medium of claim 11, wherein the high frequency radio signalcomprises a 5 GHz signal; wherein the FFT comprises a resolution of atleast 100 KHz; wherein the storage medium comprises instructions, that,when executed, cause the processing resource to determine a fourthsignal strength at a third guard frequency bin that is higher than thedirect currency frequency bin; and wherein the classification is basedon the fourth signal strength.
 15. The storage medium of claim 11,wherein the high frequency radio signal comprises a 5 GHz signal;wherein the FFT comprises a resolution lower than 100 KHz; and whereinthe storage medium comprises instructions, that, when executed, causethe processing resource to determine a signal strengths at legacy shorttraining field (L-STF) frequency bins in the FFT; and wherein theclassification is based on the signal strength at each L-STF frequencybin.
 16. A method comprising: receiving at a network device, a first FFTof a high frequency radio signal; determining, by the network device, afirst maximum strength of the first FFT; determining, by the networkdevice, a first number of peaks in the first FFT that exceeds a firstthreshold; receiving, at the network device, a second FFT of the highfrequency radio signal; determining, by the network device, a secondmaximum strength of the second FFT; determining, by the network device,a second number of peaks in the second FFT that exceeds the firstthreshold; in response to a determination that the first maximumstrength and the second maximum strength both exceed the first thresholdand a determination that the first number and the second number bothexceed a second threshold: determining, by the network device, anaverage FFT based on the first FFT and the second FFT; and classifying,by the network device, the high frequency radio signal based on a signalstrength of the average FFT at a first guard frequency bin, a signalstrength of the average FFT at a second guard frequency bin, and asignal strength of the average FFT at a direct current (DC) carrierfrequency bin.
 17. The method of claim 16, wherein the first FFTprovides a low resolution of the high frequency radio signal; whereinthe second FFT provides a low resolution of the high frequency radiosignal; and wherein the method comprises: determining, by the networkdevice, signal strengths at legacy short training field frequency binsin the first FFT; and determining, by the network device, signalstrengths at legacy short training field frequency bins in the secondFFT.
 18. The method of claim 16, wherein the normalized FFT comprises aresolution of at least 100 KHz; and wherein the classification of thetype is based on a signal strength of the average FFT at a third guardfrequency bin that is lower than the direct current frequency bin. 19.The method of claim 16, wherein the normalized FFT comprises aresolution of at least 100 KHz; and wherein the classification of thetype is based on a signal strength of the average FFT at a third guardfrequency bin that is higher than the direct current frequency bin. 20.The method of claim 16, wherein the high frequency radio signal isclassified as an LTE signal.